Striking trade unionists in Greece are forcing the shutdown of the country’s prime ancient sites, including the Acropolis, in a one-day protest over privatisation fears.

The 24-hour walkout on Thursday is expected to close the majority of Greece’s 275 archaeological sites, monuments and museums, which generate about €100m (£87m) in revenue, mostly from ticket sales, every year.

“We are doing this to protest the prospect of any of these sites being exploited by foreign funds,” said Grigoris Vafiadis, the head of the association of culture ministry employees. “Every day we are discovering that monuments have been transferred to the privatisation fund set up at the request of [bailout] lenders. No country in the world, for whatever reason, has mortgaged its cultural heritage.”

The sites, which protestors say include Knossos on Crete, are believed to have been placed on a list of properties overseen by a superfund established in 2016 with the express purpose of managing state assets for the next 99 years. The body, which also handles state asset sales, was part of the price the debt-burdened country had to pay to keep default at bay and remain in the eurozone.

Vafiadis, whose union represents more than 3,000 cultural ministry officials, mostly in the Greater Attica region surrounding Athens and central Greece, said sites were listed in the superfund by code. “It’s a long process to work out what the codes refer to on the land registry. For all we know, they might even include the Acropolis which is not just Greek but a world heritage site and should never be put in the hands of any foreign fund,” he said.

Knossos in Crete is also believed to be on a list of properties overseen by a superfund. Photograph: Doug Pearson/Getty Images/AWL Images RM

Before the strike, the finance ministry rejected the notion that popular archaeological sites were destined for privatisation. “Everything that is intended to serve public, municipal, communal or religious goals cannot be exchanged,” it said, singling out antiquities and historical sites on a list that also included nature reserves, beaches, forests, hospitals, universities and schools.

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Greece, which exited its third and final bailout in August, has fallen well short of the proceeds it has pledged to raise from privatisations in return for receiving the biggest bailout in global financial history. Since 2010, Athens has taken about €288bn in rescue loans from the EU and International Monetary Fund. At 186% of GDP, Greece still has the highest debt load of any EU member state.

The Greek culture minister, Myrsini Zorba, however, has acknowledged that mistakes may have been made in assembling the list. This week, she said she had requested the finance minister hand over a catalogue of sites, monuments and buildings that would be exempt from privatisation “to close this circle of doubt”.

“We are in a situation where not even the culture ministry knows what is on the list,” Vafiadis said. “If they accept that mistakes have been made, they should be immediately and publicly reversed which has not been the case and is why we are holding this, our first strike, as a warning.”